A buffer is made by combining 0.05 mol of a sodium acetate,0.04 mol of acetic ac
ID: 681790 • Letter: A
Question
A buffer is made by combining 0.05 mol of a sodium acetate,0.04 mol of acetic acid and enough water to make a liter ofsolution.a. What is the pH of this soltuion?
b. What is the pH after adding mol of HCl to thebuffer?
c. What is the pH after adding mol of NaOH to thebuffer? A buffer is made by combining 0.05 mol of a sodium acetate,0.04 mol of acetic acid and enough water to make a liter ofsolution.
a. What is the pH of this soltuion?
b. What is the pH after adding mol of HCl to thebuffer?
c. What is the pH after adding mol of NaOH to thebuffer?
Explanation / Answer
Formula: pH = pKa + log [salt] / [ acid] As the volume is same concentration can be replaced by No. ofmoles. pH = p Ka + log ( No.of moles of salt / No.of mole sof acid) a ) pKa for acetic acid = 4.74 Upon substituting the data in theequation, pH = 4.74 + log ( 0.05 / 0.04 ) =4.83 b ) When a strong acid like HCl is addd to the acidic buffer,no.of moles of acid increases and no.of moles of saltdecreases. But in this case Number of moles of HCl is more ( 1mole) than the salt(0.05 mol) and acid(0.04)respectively. So the pH is purely depends upon the acid. CH3COONa + HCl --------->CH3COOH 0.05 1mol 0 0 0.05 0.05 So in the solution there will be 0.05 moles of HCl and (0.05 +0.04 ) moles of acetic acid. But compared to strong acid weak aciddissociation can be neglected. [H+] = 0.05 mol / 1 L = 0.05 M pH = - log[H+] = 1.3 c) When a strong base like NaOH is addd to theacidic buffer, no.of moles of acid decreases and no.of moles ofsalt increases. But in this case Number of moles of NaOH is more ( 1mole) than the salt(0.05 mol) and acid(0.04)respectively. So the pH is purely depends upon the base. c) When a strong base like NaOH is addd to theacidic buffer, no.of moles of acid decreases and no.of moles ofsalt increases. But in this case Number of moles of NaOH is more ( 1mole) than the salt(0.05 mol) and acid(0.04)respectively. So the pH is purely depends upon the base. But in this case Number of moles of NaOH is more ( 1mole) than the salt(0.05 mol) and acid(0.04)respectively. So the pH is purely depends upon the base. CH3COOH + NaOH ---------> CH3COONa +H2O 0.04 1 0 0 0.06 0.04 [OH-] = 0.06 M pOH = 1.22 pH = 12.77 pH = 12.77Related Questions
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